As the demand for high speed and high integration of a semiconductor device increases, a trend in a line width of a semiconductor shows a rapid decrease. However, a decrease in line width in an ultra large scale integrated circuit semiconductor device leads to an increase in RC delay, which is the result of capacitance (C) between metal wirings and resistance (R) of the wiring metal, thereby decreasing the operating speed of the device. In order to address this issue, there were efforts to replace aluminum as a conventional wiring metal with a material having lower resistivity than that of aluminum, and resistance problems of the wiring metal were resolved when IBM produced a microprocessor using copper as a wiring material in 1997. As for the capacitance, a silicon oxide film, which was conventionally used as an insulator, has permittivity of about 4.0, however, interference between wirings could not be prevented due to an increase in capacitance as the line width decreased. As a result, the development of an interlayer dielectric material that addresses this issue has been actively pursued.
For this interlayer dielectric material to be applied to actual semiconductor processes, a number of integration characteristics besides low permittivity should all be satisfied. Required properties appropriate for a process, such as electrical isotropy for wiring design and process facilitation, low reactivity with a metal wiring material, low ion transferability, chemical mechanical polishing (CMP), etc., should all be satisfied.
For a copper wiring process related to thermal characteristics to maintain thermal stability at a temperature up to 400° C. and facilitate heat emission during the operation of a device, thermal conductivity approximating to that of a silicon oxide film (12.0 mW/cm° C.) should be required including a low thermal expansion coefficient (<10 ppm/° C.), which may inhibit the change of the film according to a change in temperature. Further, low leakage current and high breakdown voltage are required as electrical properties. In addition, various stresses which may occur at the interface with another material, adhesion which minimizes peeling, crack resistance, etc., should be satisfied and hygroscopic property, which leads to an increase in permittivity, should be low. In addition, compatibility in the unit process, such as polishing processability, should be maintained when the CMP process is performed with at an appropriate strength. Among these characteristics, in relation to compatibility with the mechanical polishing process such as CMP process, the development of an ultralow dielectric film, which may withstand the process and maintain a high elastic modulus of 5 to 6 GPa or more, has been an issue. When pores are introduced in order to reduce permittivity in conventional ultralow dielectric films, a low mechanical strength of less than 5 GPa is exhibited and thus attempts to overcome this have been actively performed.
Research and Development and commercialization by Dow Chemical, Applied Materials, Rohm&Haas, JSR Micro, ASM, Allied Signal, etc., are continuously developing an ultralow dielectric material.
Among the above stated companies, Dow Chemical Company has been continuously developing SiLK™ film for the past few years, which the coefficient of thermal expansion (CTE) of the film exceeds 50 ppm/° C. in addition to its mechanical strength. Subsequently, IBM has actually stopped the application of the film during processes. Even though IBM stopped the process application due to a CTE issue of SiLK™, Dow Chemical Company has continued the development of the SiLK series while improving the CTE. Recently, Dow Chemical Company has developed a porous SiLK™, called SilK Y resin having a pore size of about 1.8 nm and permittivity of 2.2. However, since porous SiLK™ has an elastic modulus of 3.0 GPa, which is generally low and the CTE of the film is still as high as 40 ppm/° C., it is unclear whether the film can be applied to actual processes [Silk Semiconductor Dielectric Resins, (http://www.dow.com/silk)]. Although, it is known that Fujitsu, Sony, and Toshiba from Japan mass produce the resin by using the SiLK™ thin film, and these companies are adopting a hybrid structure of CVD and SOD films during the integration thereof. Most of the other companies have developed low dielectric materials by changing the structure of the raw material into a material based on methylsilsesquioxane (MSQ), and most of the rotation coating type low permittivity materials developed by Rohm and Haas, JSR Micro, Allied Signal, etc., have an elastic modulus of 3 GPa in the range of 2.1 to 2.3 as the minimum permittivity.
Black Diamond from Applied Materials, which is a material with a carbon doped oxide (CDO) structure previously mentioned, and Aurora RULK having permittivity of 2.6 to 2.7, are produced by chemical vapor deposition (CVD), and both of them have an elastic modulus of about 8 GPa [Nanotechnology Forum 2005]. In Korea, Samsung Advanced Institute of Technology prepared an ultralow dielectric film by using a cyclodextrin having an alkyl group or an acetyl group at the terminal thereof, and LG Chemical Ltd., prepared an organic silicate matrix to prepare a nanoporous organic silicate. However, presently, there has been rarely any study on low permittivity materials.
With respect to this, the present inventors prepared a chemical reaction type pore-forming resin by using an organic cyclic polyol and an organic non-cyclic polyol, which can also use the resin to prepare an ultralow dielectric film having excellent mechanical properties as the pore content of the resin increases, unlike conventional nonreactive porogens, for example, polycaprolactone, Tetronics, methyl cyclodextrin, etc. [Korean Patent No. 589123, Korean Patent No. 595526, and Korean Patent No. 672905].
However, there still exists a need for an ultralow dielectric film having significantly improved mechanical strength and permittivity, while being able to substitute as a SiO2 dielectric film currently being used and is available for the next generation semiconductor.